Hitherto, various endeavors have been made in order to enhance the performance of high impact resins. For example, U.S. Pat. No. 4,690,986 discloses that, with a notice given to lowering in glass transition temperature and modulus of elasticity of a rubber layer, investigation was carried out to utilize polyorganosiloxane rubbers having both a low glass transition temperature and a low modulus of elasticity as a rubber source for the high impact resins. However, this method cannot improve a mat and bad surface appearance owing to the polyorganosiloxane rubbers. Also, when such the rubbers are used, their small particle size lowers the impact resistance, so that those having a large particle size are used.
In order to improve the surface appearance of resin molded products, U.S. Pat. No. 4,894,415 proposes a compound rubber graft copolymer produced by graft-polymerizing a vinyl monomer onto a compound rubber comprising a polyorganosiloxane rubber and a poly(meth)acrylic rubber.
Also, Japanese Patent Application Kokai No. 62-280210 proposes a graft copolymer composed of the core of a crosslinked silicone rubber, the first shell of a crosslinked acrylate rubber and the second shell comprising the graft component of a vinyl polymer.
Further, U.S. Pat. No. 4,885,209 proposes a graft polymer produced by graft-polymerizing an ethylenic unsaturated monomer onto a rubber comprising the core of a crosslinked acrylate rubber, etc. and the shell of a polyorganosiloxane.
However, in the specifications of Japanese Patent Application Kokai No. 62-280210 and U.S. Pat. No. 4,885,209, reference is made to the graft polymer having a number average particle size of 0.05 .mu.m or more, but the examples of the specifications disclose only those having a particle size as large as 0.15 to 0.42 .mu.m, making completely no reference to a specific means for producing those having a particle size of 0.10 .mu.m or less.
Also, a compound rubber graft copolymer disclosed in U.S. Pat. No. 4,894,415, because of its compound rubber component having a particle size larger than 0.07 .mu.m, is poor in colorability by addition of pigments, so that it is low in commercial value. Because of this, there is a strong demand for the development of high impact resins having both a good impact resistance and an excellent colorability by addition of pigments.
The present inventors have made an extensive study on a relationship between the particle size and colorability by addition of pigments of the graft copolymer. As a result, they have found that by using a polyorganosiloxane having an extremely small particle size and producing the compound rubber of this polyorganosiloxane with a poly(meth)acrylate rubber, having an extremely small particle size, the graft copolymer particle obtained from this compound rubber shows both an excellent impact resistance and a good pigment colorability.